Anodising AZ31 in a Phosphonium Ionic Liquid: Corrosion Protection through Composite Film Deposition

Abstract

Magnesium alloy AZ31 was anodised in the ionic liquid (IL) trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P 6,6,6,14][(iC8)2PO2]) under potentiostatic control to a relatively low voltage of 18 V using current densities of 0.05, 0.1 and 0.5 mAcm-2. The formation of these films on as-polished AZ31 made no significant change to the corrosion performance in 0.01 M NaCl. Film stability and corrosion protection of the AZ31 alloy was increased when surfaces were anodised after an acid pickling pre-treatment in a mixture of nitric and phosphoric acid. ToF-SIMS revealed both the anion and cation of the IL were present in the film, with greater deposition observed on the pickled anodised surfaces as opposed to as-polished. Copyright © 2012 The Electrochemical Society.